Single-Photon Source With Cross-Polarized Waveguide Coupling
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Solution Overview
Problem
Existing single photon sources (SPSs) face challenges in ensuring deterministic emission of photons with minimal time uncertainty, particularly due to the need to separate the driving laser from the single photon emission in resonant optical excitation schemes.
Innovation Solution
The solution involves using an asymmetric quantum dot (QD) integrated within a photonic crystal structure, where the QD is excited and photons are collected using waveguides oriented at 45° to the QD's axes, allowing for orthogonal polarization directions for excitation and emission, thereby enabling efficient Purcell enhancement and directional emission of single photons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional light sources (lasers, LEDs, bulbs) are used, then they can emit light, but they emit many photons at once which cannot be used for quantum key distribution
Solution Approach 1:
The patent segments the light emission process by using a weak laser beam that emits photons one at a time through a time-varying optical element, dividing the continuous light stream into discrete temporal slots where only one photon can exist at a time, thus converting a multi-photon source into a single-photon source suitable for QKD
2Reliability
If single photons are emitted one at a time, then quantum key distribution becomes possible, but the data transmission rate becomes very low
Solution Approach 1:
The patent employs periodic action by rapidly switching the optical element (acousto-optic modulator or electro-optic modulator) at high frequencies to create periodic single-photon emission intervals, allowing multiple single photons to be emitted in sequence at high rates while maintaining the single-photon property for QKD
Solution Approach 2:
The patent changes the temporal parameter of photon emission by using time-varying optical elements to control when photons are emitted, transforming the emission from continuous to discrete temporal packets, thereby enabling high-rate single-photon generation suitable for both QKD and high data transmission rates
3Illumination intensity
If optical amplifiers are used to boost signal strength, then signal can be amplified, but they create multi-photon states that are vulnerable to attacks
Solution Approach 1:
The patent introduces time-varying optical elements (acousto-optic modulators, electro-optic modulators) as intermediaries between the laser source and the detection system, which control and shape the photon emission temporally to ensure single-photon states without requiring optical amplifiers that would create multi-photon states vulnerable to attacks
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves high-efficiency, deterministic single photon emission with reduced time uncertainty, enabling high repetition rates and improved performance in quantum applications such as quantum key distribution and on-chip quantum computing.
Implementation Method 1
The weak laser beam is switched on and off at a high frequency by an acousto-optic modulator or electro-optic modulator
Implementation Method 2
The weak laser beam is switched on and off at a high frequency by an acousto-optic modulator or electro-optic modulator
Implementation Method 3
A single photon source is a device that emits exactly one photon at a time
Data Source
Figure 1a~2b
Figure 3~4b
Figure 5~6
AI summary
A single photon source comprises a photon emitter (10), an excitation waveguide (30) arranged to direct excitation photons having a first polarisation direction into the photon emitter, and a collection waveguide (42) arranged to collect photons having a second polarisation direction from the photon emitter. The first polarisation direction is coupled to a first exciton state of the photon emitter and the second polarisation direction is non-parallel to the first polarisation direction and is coupled to a second exciton state of the photon emitter, and the first and second exciton states have substantially equal energies.